This invention relates to food product packaging and equipment, and, more particularly, to food product packaging which requires vacuum packing.
In many operations utilizing a machine for hermetically sealing food product trays or packages which are to be heat processed or pasteurized, the product will be sealed under vacuum.
Sealing under vacuum offers many advantages over simple hermetic sealing of a container. Sealing under vacuum causes a greatly reduced oxygen (O.sup.2) concentration in the packaged food product. This has been shown to improve preservation or shelf life time significantly for most packaged food products, even for those which have not been subsequently pasteurized.
A separate advantage of vacuum sealing exists for those products that will be subsequently heat processed and sterilized, such as through a pasteurization process. Vacuum sealing reduces the total gaseous component of the container and, thus, reduces the likelihood of an excessive pressure buildup from air within the container expanding during the heat processing. Consequently, there is less likelihood of the container being separated or split at a seal by such generated internal pressures. This is particularly true for plastic or cardboard trays and packages which are sealed with plastic film, as such containers are the most fragile and would be the most susceptible to damage from internal pressures.
In one such packaging system, utilizing plastic film sealed over the containers, and utilized, for example, in the packaging of surimi products into packages, or trays, the surimi or food product is distributed to wells in plastic trays, along with a sauce or condiment component in an adjacent well. This tray is covered conventionally, with a plastic film, and is then sealed under vacuum before being conveyed to a pasteurization line. The shelf life of such vacuum packed, hermetically sealed and pasteurized products is exceedingly long, with product quality remaining high.
The conventional sealing apparatus for applying plastic film to such plastic trays utilizes heat sealing under vacuum, with subsequent pasteurization. To facilitate the overall speed of the packaging operation, the film is laid over the trays, and the heat seal is subsequently applied under vacuum, in a moving conveyor environment. The conveyor has tray supports carried on and movable with the conveyor, with a plurality of trays supported thereon. The vacuum heat seal must be applied, then, under such circumstances that the sealing means will duplicate the movement of the conveyor. The conveyor chain carries the tray supports as a series of connected units. Each such unit is conventionally a steel plate, or platter, with depressions or wells for supporting the trays, and which also support the trays when the trays are contacted by the film sealing means.
A reciprocating system is used wherein the vacuum chamber is part of a vacuum assembly on a frame which shuttles back and forth along the conveyor line. The vacuum chamber extends over the trays, and clamps down around, and encapsulates, a conveyor platter (the tray support) holding the food product tray. The vacuum assembly then reciprocates relative to the movement of the conveyor. The frame moves initially with the conveyor and continues to encapsulate the conveyor platter until the sealing can be completed.
Sealing occurs only after the desired amount of vacuum has been drawn. A heated platen comes down within the vacuum chamber and seals the plastic film to the edges of the plastic tray. By utilizing such a reciprocating system, the sealing operation is performed on trays which are continuously in motion along with the principal conveyor. Hydraulic or pneumatic systems with suitable controls are utilized to coordinate the movements of the vacuum chambers with the direction and speed of the conveyor and trays, and such systems can also control the application and timing of the vacuum and heat sealing operations. After sealing is completed, the chambers release the conveyor platter and shuttle back against the direction of movement of the conveyor to a position where they are ready to encapsulate another platter and repeat the vacuum and sealing operations.
In the known vacuum shuttle assembly, the frame includes plural vacuum chambers which are utilized simultaneously, each of the chambers having heated platens which come down inside the chamber to form the seal on multiple trays which are sealed during a single shuttle. The vacuum source is provided by a vacuum pump, which is connected by a conduit to a vacuum manifold, and through this manifold to both the upper and lower chambers. In this known packaging apparatus, the vacuum manifold is kept near the vacuum pump in a stationary matter. The manifold draws the vacuum from the plural upper and lower vacuum chambers through separate conduits, or hoses.
Difficulties arise in pulling an equal amount of vacuum through each of the hoses. As the reciprocating heat sealing apparatus moves back and forth with the conveyor, the hoses from the manifold are themselves flexed and are moved back and forth through different hose lengths, depending on which chamber a given hose leads to. When the vacuum is drawn, it is important that the vacuum in each upper and lower chamber be equivalent in order that the sealing of the plastic film to the trays will proceed in an efficient and unimpeded manner. It is difficult to maintain this level of consistency with this known arrangement.
Among the objects of this invention is to provide an improved system for heat sealing plastic film to food product trays under vacuum, and which can be used to vacuum seal continuously conveyed trays.
A more specific object is to provide such an improved system as part of an apparatus which follows the movement of the tray conveyor and does not suffer any loss in the amount of vacuum or in the strength or integrity of the subsequent seal as a consequence of the apparatus movements.
A further object is to provide such a vacuum system that will consistently pull a strong, even vacuum among the upper and lower vacuum chambers of such a reciprocating heat sealing apparatus.